Process of recovering molybdenite by froth flotation



Sept. 16, 1941.

T. A. JANNEY ETAL PROCESS OF RECOVERING MOLYBDENITE BY FROTH FLOTATION Filed Jan. 9, 1939 2 Sheets-Sheet 1 Copper Mill Molybdenite and Non-metallic Ganque Minerals p B Thickzner 13 2 C Filter 0 Aqinq, "1.2., Heatinq,

Steaminq, Drqinq, elc. Sulphuric Acid, p I I ialneieslsgnihand UPQI" A c0 0 r0 er Gcmque Flolalion E l l pH under 8 Ganque Concentrqle Talc- Chlorite and Sericile To Waste olher Alkali to increase H Kerosene, Alcohol frotner and Llme or Molqbdenite Flotation I pH '5 /0 pH ll J Molqbdenitz Concentrate maybz draped/0M6?! it'desired) Tallinqs producl consist- L mg Princlpollq of Copper 6 d lron Sul hides.

To Morkel" on p Feed (Heading) lnsoluble Rouqher 1 Insoluble Float 2 Insoluble Cleaner v I l J l'lnsoluble Sink q er Cleaner I Concenl'rcl'c I 4 Tao/mas A. JAN/YE), Rouqher- ALPHA 6../0///V50/Y. and Tunings Clappe 67/42; 44. A O/KE'S,

Tmlmqs INVENTORS; BY M%/A- M/ l W ATTORNEYS p 16, 1941. T. A. JANNE'Y Em 2,255,776

PROCESS OF RECOVERING MOLYBDEN-ITE BY FROTH FLOEATION 7 Filed Jan. 9, 1959 2 Sheets-Sheet 2 Mo 52 m TAlLms AMI/,4 0. Jail/V3017. and

(mews M A o/a s. BNVE NT OI2S;

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Patented Sept. 16, 1941 UNITE.) STATES JUN 161942 Eassurs PATENTMCFFICE raocrss or nscovnanvo 'monvnnmrs av morn FLOTATION Thomas A. Janney, Garfield, Alpha G. Johnson, Magna, and Charles M. Nokes, Salt Lake City,

, Utah Application January 9, 1939, Serial No. 250,014

13 Claims. (01. 209 166) lybdenite is a mineral which floats readily, due

principally to its non-polar character, its nonoxidation, and to its micaceous habit. The recovery of molybdenite as a low-concentration product presents little difliculty, but considerable dimculty has been experienced in obtaining a high purity molybdenite concentrate by any hitherto-suggested procedure, without loss of an important percentage of the mineral in the recovery process. The copper and iron sulphides, for example, tend to float with molybdenite, as do certain gangue minerals, such as those of the talcose and chloritic type, all of which factors contribute to the difl'iculty of securing a high grade molybdenite product.

The present invention is directed to the recovery of molybdenite by methods involving selective froth flotation, providing for the separation and recovery of that mineral from concomitant metallic and non-metallic contaminants to a higher degree than has been hitherto considered possible consistent with a high total recovery.

Under standard flotation conditions, with a given set of reagents and a given set of minerals in the material being treated, there will be a definite relation of flotation order (floatability) between the variousminerals of the mineral aggregate, i. e., the several minerals will follow a certain scale of floatability. It is frequently necessary, in order to effect proper separation of such minerals, to alter this order of floatability, or to accentuate differences therein as by increasing or decreasing the selectivity index. This alteration is'usually secured by the addition of certain reagents, such as the addition of lime and cyanide to depress pyrite and thus increase the. selectivity index between chalcopyrite and pyrite, for example.

Where molybdenite is secured as a concentrate,

,by flotation thereof along with other sulphide minerals, and often contaminated with nonmetallic minerals, considerable difliculty has been concentration. For example, if a sulphide, ore

flotation concentrate containing about one per cent molybdenite, 30 per cent copper, and 25 per cent iron is refloated, there will be no significant change in the proportions of these minerals. It becomes necessary, therefore, to change the scale of floatability of these sulphide minerals. which is accomplished according to this invention by subjecting the minerals to an aging treatment, which will serve to depress the floatability of the sulphide minerals other than molybdenite. This aging treatment is one which will secure the production of an inhibitory agent or condition which will depress the floatability of the sulphide minerals other than molybdenite, and preferably is one which will effect an at least partial oxidation of such other minerals (molybdenite being not readily subject to oxida-- tion), to efiect a surface tarnishment of such other mineral particles. The treatment is preferably also such as to secure a substantially complete removal, as by decomposition, of the concomitant flotation reagent or reagents remaining from the previous flotation operation, if the material has been subjected to a previous flotation treatment, in order that a subsequent flotation of the product in the recovery of the molybdenite will not be influenced by any agent tending to secure or facilitate collection of the other sulphide minerals.

Where the molybdenite material is also contaminated with difllcultly separated gangue materials, such as those of the talcose and chloritic types, it is further necessary to modify the order of floatability of the minerals to the end that the gangue material is eflectively removed without loss of molybdenite. In this connection, a further object of the invention is to provide a flotation procedure for the removal of such contaminating gangue materials from a molybdenitecontaining mineral aggregate, followed by a separation of the molybdenite from the other sulphide minerals.

An important object of the invention is to provide for the recovery of molybdenite from a mineral aggregate containing other metallic sulphides, involving the aging of the aggregate to decrease the floatabflity of such other sulphides and thus facilitate the separation of molybdenite therefrom.

A further object of the invention is to provide a process of separating molybdenite from a mineral aggregate containing other metallic sulphides and a non-metallic gangue, involving the experienced in securing a further separation and 55 aging of. the aggregate to change the order qt the character of the mineral aggregate under-- going treatment, for example, where the sulphide minerals other than molybdenite are in a fairly advanced stage of oxidation, a relatively mild aging treatment is adequate; wherethe I aggregate is one in which the sulphide minerals other than molybdenite are'practically free of primary oxidation, a more drastic aging treat* 1 ment is necessary. The Chino Copper Company general mill concentrates (from the Chino opera- ,tions of the Nevada Consolidated Copper Company) are illustrative of the first class of mineral the gangue away from the sulphide minerals, including molybdenite, while maintaining the pulp on the acid or faintly alkaline side, i. e., at a pH below 8, and the tailing's from that flotation treatment are then subjected to further flotation in the presence of a collector for molybdenite, at a pH greater than that of the previous flotation land in any event greater than 3, in which the molybdenite is recovered in the froth and the other sulphide minerals remain almost entirely in By this procedure concentrates runningin excess of 90 per cent M082 have been obtained, with as low as 0.25 per cent copper.

In connection with the above typeof procedure, the desirable pH value for the gangue'flotation step may in some cases be obtained as a result of the production of acid compounds in heating aggregates, and the Utah Copper Company concentrates (from the operations near Garfield, Utah)' are illustrative of the second class.

For the treatment of the materials, the aging operation may comprise heating, atmospheric present as a result of the preliminary concentration, the character of the aging will be controlled by the ease or difliculty with which such reagent or reagents may be eliminated. For example, a

collector such as butyl xanthate 'which' is quite useful in the treatment of the fairly well oxidized mineral aggregates, may readily be decomposed, whereas with the purely sulphide mineral types of aggregate a collector such as sodium dicresyl dithiophosphat'e "is frequently necessary, which will necessitate a somewhat drastic heat',treat-' ment in order to decompose it. For the proper aging of the purely sulphide aggregate, therefore,

heating for a relatively long period at temperatures aslow as 300 F., or a short heating at temperatures as high as 700 F. are useful, for example, a heat treatment at 450 to 550 F. for a few minutes (fifteen minutes, for example) is effective to secure both the partial oxidation or tarnishment and the removal of the more stable reagent. This specific temperature range is not essential, however, inasmuch as practically any heating operation, if continued for asuflicient time, and in the presence of oxygen such as from atmospheric air, will efiectthe desired aging.

The temperature limitations will obviously be dictatedby the expediency of the operation at a particular location and by the availability of equipment.

For the separation of molybdenite from 'an aged mineral aggregate having a relatively low content of insoluble gangue, flotation with any desired collector for molybdenite (such as kerosene) and a frother, preferably an alcoholic frother, will cause the molybdenite to be collected in the froth and the other sulphide minerals to remain principally in the tailings. Concentrations up to about 95 per cent M082 have been obtained in this manner.

For the separation of molybdenite from a material containing readily floatable gangue ima- -terials,such as those of the talcose, chloritic, 'or

micaceous types, a somewhat modified procedure is followed, in which the aged material is first subjected toa flotation treatment to float gangue, was subjected to test.

orrother agingsprocess employed, although it will be realized that addition-a1 acid such as sulphuric or an alkaline reagent such as lime, may be added, if necessary, to establish the pH- value at the desired point.

As a specific illustration of the practice of the invention on a mineral aggregate containing a low proportion of difficultly removed insoluble gangue. in which the sulphide minerals were in a fairly advanced stage of oxidation and illustrative of the first class of materials, a concentrate fresh from production at Chino Concentrators, Nevada Consolidated Copper Company, containing approximately oneper cent Moss, per cent copper, 25 per cent iron, and 4 per cent This concentrate, when refloated immediately, without aging'treatment, showedno separation of molybdenite from its associated minerals. Various aging procedures were carried out, rangingfrom (a) atmospheric drying, (b) heating in water, (0) drying on a steam hotplate, (d) drying on a steam hotplate followed by continued heating after reaching dryness, (e) passing live steam into the pulp and maintaining boiling temperature for thirty minutes, and (f) allowing the pulp to stand in native water for periods ranging from 24 to 192 hours. In each case flotation subsequent to an aging treatment resulted in the production of a molybdenite concentrate containing at least tentimes as much molybdenite as the feed material, and in all tests except two the m0- lybdenite proportion in the concentrate was in excess of 40 per cent, and for the most part in excess of 60 per cent, while in the case of the steam hotplate-dried material which was heated further after reaching dryness (procedure d) a flotation procedure without pre-treatment, and

- an Insoluble float" the other sample being subjected to a four-hour drying at C. prior tothe flotation process. The accompanying drawings, Fig. 1, maybe used to visualize the flotation treatment, in which the feed was subjected to flotation with an alcoholic frother at i which is designated as the "Insoluble rougher. The frother from this treatment was subjected to a cleaning operation at 2, producing which was discarded as waste,- and an Insoluble sink which was returned to the circuit for further treatment. The

riched in Mesa and which had undergone heat treatment to secure the desired aging. A flotation procedure such as that outlined in Fig. l was practiced, the Insoluble float produce representing the froth product from the rougher I,

the Rougher tailing product representingthe The results of the above tests are set forth in the following Table I, in which the various products are designated as above set forth, showing the percentages of copper, insoluble material and molybdenite with their percentage distribution.

Table I Test #1 Test #2 g 'igg' Heat-treated Orig. came. om Procedure odmfiom emoval of Orig. cone. insol. conc. dried 4 hours by alcohol at 195 C. lrother and Float. same removal as in Test $1 M081 cone. by kerosene and pine oil Hea ng (my):

Percent Cu 34. 50 34. 50 9. 00 9. 00 Percent MoS: i 1. 57 l. 57 Insol. float:

48. 98 i. 87 37. 50 1. 80 54. 24 09 2. 40 89. 80 12. 86 19. 20 30 12 k 9. 86 13 Percentwt 44.88- .92 Percent Cu 32. 80 30. 95 Percent dist Cu 43. 51 81 Percent 12. 2o 18. 2) Percent dist insol. 60.67 1.94 Percent Mos: 2. 81 l. 07 Percent dist. M081 84. 58 63 R0. tailing:

3.23 91.02 10. 00 35. 90 95 94. 72 Percent insol 47. 20 7. 00 Percent dist. insol. 16. 70 72. 80 Percent M081... 27 04 Percent dist. M081..- .60 2. 26 Cl. conct. (MoSz):

Percent wt 1. 63 1. 94 Percent Cu 14. 65 5. 90 Percent dist. Cu 71 12 Percent insol 19. 80 7. Percent dist. inso 3. 52 l. 60 Percent MoS: 3. 90 73. 40 Percent dist. M081... 4. 29 89. 56 C1. tailing:

Percent wt l. 33 4. 25 Percent Cu. 15. 20 34. 70 Percent dist 59 4. 26 Percent insol 42. 80 9. 20 Percent dist. insol... 6. 26 4. 46 Percent MOS: 73 2. 78 Percent dist. MoSz 67 7. 42

It will be seen that the heat treatment (aging) was beneficial from several standpoints, namely, there was a greater rejection of copper and insoluble into the Rougher tailing, a. larger accumulation of molybdenite in the Cleaner concentrate (on the basis of total recovery) and a higher degree of purification in the final product.

The data shown in the following Table II illustrates the efiect of pH control in the insoluble flotation and the molybdenite flotation. The material treated represents a mill concentrate enwaste material from rougher 3, the Cleaner tailing" representing the tailings product from the cleaner 4, and the "Cleaner concentrate" representing the float material from the cleaner 4. The procedure diifered from that used to obtain the data shown in Table I only in the respect that lime,was added at rougher 3 to put the 'pI-I of the pulp on the basic side for the data shown in the right-hand column (Test 4) while the pH of the pulp was unchanged for the data shown in the left-hand eoluinn (Test 3).

. Table II Test No. 3, Test No. 4, no lime lime for for M08; M05,

Heading:

Percent Cu 9. 11 9.11 Percent insol" 44. 40 44. 40 Percent M08 23. 82 23.82 0. inscl. floa 11 5. 55 5. 55 ercent wt 22. 34 22. 96 Percent Cu- 2. 74 3. 88 7. 56 10. 76 81. 58 81. 67 41. 53 41. 88 Percent M08 1.82 1.89 Percent dist. M08 1. 75 1.88

N o lime Lime added here added here R0. tailing:

pH 5. 55 9. 18 Percent wt 4a is 47. 70 Percent Qu 13. 25 13. 66 Percent dist Cu 79. 05 78. 72 Percent insol. 44. 98 46. 22 Percent dist. inso 49. 41 49. v Percent M05, 5. 84 2. 20 Percent dist. MoS; 12 00 4. 59 Cleaner tailing:

9. l9 7. 22 10. 98 ll. 28 12. 52 9. 79 32. 05 35. 61 6. 72 5. 82 20. 14 15. 47 7. 90 4. 90

None 8.3 Kerosene 2. 15 2. 15 Alcohol i'rother 67 67 Fig. 2 of the accompanying drawings-illustrates a flow sheet indicating typical-steps in the process for treating mineral aggregates carrying a relatively large proportion of gangue material, and referring thereto, a source of partially concentrated molybdenite-containing sulphide mineral is indicated at A, from which materialis drawn into a thickener B and thence to a filter C. The filtered mineral is withdrawn from the filter C and subjected to an aging operation at D to cause the order of fioatability to be altered, as

above described, whichoperation may comprise Sulphuric acid may be added at this point, if necessary, to lower the pH of the pulpto a value below 8 and preferably to a value in the range of pH 3 to pH 8, together with a suitable frother (such as an alcohol frother of the type marketed by the Du Pont de Nemours Company under the trade symbol B-22). The pulp is then subjected to flotation at E, to separate the gangue subjected to a further flotation as at F. in which operation the molybdenite is recovered in the froth and the iron and copper sulphides are kept in the tailings. The sulphide tailings G may be treated for the recovery of the copper values by conventional smelting procedure, as will be apparent to one skilled in the art. The molybdenite concentrate from F, indicated at H, will be of high grade, and constitutes a mar- 'ketable product.

neighborhood of 11. The tendency for copper to float with the molybdenite gradually increases to a certain pH, generally in the neighborhood of to 6, then decreases with a further increase of pH up to a certain value, generally in the neighborhood of pH '7 to pH, 9, and then increases. The optimum pH in the molybdenite flotation operation, therefore, will be seen to be dictated by the character of the concentrate desired.

.The character of the aging treatment affects the optimum pH in the molybdenite flotation operation, and, in general, the more rigorous the aging treatment, the lower the optimum pH from,

the standpoint of both MOS: recovery and cop.- per rejection. I

Figs. 3 to 5 illustrate the above general prim- I ciples graphically. The values givenin these fig- It will be appreciated that the scheme out-" lined in Fig. 2 may also be applied to the treatment of a molybdenite-containing mineral aggregate containing a nominal amount of gangue, by omitting the gangue flotation step, i. e., by passing the material from step D directly to step Fl, without intermediate flotation of the insolu les.

The pH of the insoluble and molybdeniteflotation circuits is variable, and the optimum pH for a specific flotation procedure will depend upon the character of the feed and uponithe nature of the aging treatment given such feed. In general, the lower the pH in the insoluble float, the better the inhibition of the flotation of the molybdenite. The use of a pH of much less than 3.0 in the insoluble flotation circuitis ordinarily impracticable, due both to the highly corrosive nature of the pulp at such values, and to a partial reactivation of the copper and iron sulphides which apparently results from solution of the tarnished surfaces. Where acid-proof equipment is employed, .values less than pH 3.0 may be utilized, and, similarly, where the float from the insoluble flotation is to be returned to treatment for recovery of copper values, pH values less than 3 are fully operative in the insoluble circuit. r

Furthermore, the proportion of insoluble" in the feed will afiect the optimum pH in the insoluble flotation step and the molybdenite flotation step; for example, a high insoluble content in the pulp will have the eflect of inhibiting the flotation of M032, wherefore a higher pH may be utilized without undue loss of MOS: in the insoluble float than could be utilized where'the insoluble content was low, but the presence of a high insoluble residue in the tailings from the insolu ble flotation operation would likely require a.

more alkaline condition in the subsequent molybdenite flotation to keep down flotation of insoluble with the M082 in the production of the M082 concentrate. These conditions, and the eflect thereof on the preferred practice of the inventionwill be apparent to those skilled in the flotation art.

The activation of MOS: in the succeeding molybdenite flotation increases toward a pH in, the

ures are for a particular feed, namely, one in l which the sulphide minerals were practically free of primary oxidation, and are ofiered as examples only, as diflerent values would result if a different feed were employed, or if difierent aging treatments were used.

Fig. '3 illustrates the variation in the loss of M05: in the tafling product of the molybdenite flotation, and the copper contamination of the concentrate from such flotation, as the pH of the molybdenite flotation is varied between 2.9 and 10.8 (the previous insoluble flotation being conducted at pH 2.9 in each instance). It will be seen that the M082 loss is least at from pH 5 to pH 8, while the copper contamination reaches a maximum at pH 6, drops to a minimum at pH 8.8 and again rises with an advance of pH.

Figs. 4 and 5 represent, respectively, the Moss loss in the tailing and. the copper contamination in the concentrate, at different pH values for the molybdenite flotation (rougher operation), the solid line curves representing the values obtained when the feed material (Utah Copper Company general mill' concentrate) had been aged by roasting for thirty minutes at 450 F. The broken line curves represent the values obtained when the feed material was subjected to a re-roast of thirty minutes at 475 F. before flotation. From these curves it will be seen that the maximum MOS: recovery takes place at the high pH values and the optimum copper rejection is at intermediate values. The curves for the roasted and re-roasted materials have a general similarity as to trend, but there isa better MoSz recovery and a better copper rejection at a given pH for the re-roasted feed than for the once-roasted material.

The present inventionis not to be considered as limited to the specific embodiments herein described, but rather to the scope of the subjoined claims. The pH desired for the insoluble float may be obtained for the most part as adirect result of the aging treatment, due to the formation'of products of acid reaction in the at least partial oxidation resulting from such aging, although additional acid such as sulphuricacid may be added to the pulp if desired. The pH of v carbonate or hydroxide may be added to the pulp to bring the pH up to any desired value alkali hydroxides, or lime for the purpose of raising the pH of the material for the molybdenite flotation, .to establish a pH greater than that of the insoluble flotation circuit and not in excess of pH 11.- The pH in the M082 circuit should not reach excessively high values, becausehere this mineral tends to resist flotation and thus a loss through tailing discharge would result. The specific flotation procedures are described as including thefluse of alcoholic frothers, and while it has been found that alcoholic frothers of the aliphatic monohydric type, and particularly those having a carbon atom range of to 7, are especially useful in the present invention, it will be appreciated that other frothers may be found equally effective, and may be used to carry out the present invention.

The subject matter of this application pertaining particularly to the treatment of molybdenite-containing mineral aggregates including sulphides of other metals which are in a fairly advanced stage of oxidation is more fully set forth and specifically claimed in our copending application Serial No. 350,162, filed August 2, 1940, for Process of recovering molybdenite by froth flotation.

We claim:

1; In the separation of molybdenite from a mineral aggregate including other sulphides such as iron and copper sulphides, and gangue materials, by froth flotation, the improvement which comprises: subjecting such a mineral aggregate to a heating treatment at a superatmospheric temperature in the presence of oxygen to effect an oxidation of such other sulphides, said treatment being ineffective to cause substantial oxidation of such molybdenite and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite, and then subjecting the so treated aggregate to froth flotation to recover the molybdenite therefrom.

2. The improvement set forth in claim 1, in which such heating treatment comprises roasting the aggregate at a temperature in the neighborhood of from 300 to '700 F.

3. In the separation of molybdenite from a mineral aggregate including other sulphides such as iron and copper sulphides, and gangue materials, by froth flotation, the improvement which comprises: subjecting such a mineral aggregate to an oxidation treatment at a superatmospheric temperature in the presence of moisture to effect an oxidation of such other sulphides, said treat ment being ineffective to cause substantial oxidation of such molybdenite and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite, and then subjecting the so treated aggregate to froth flotation to recover the molybdenite therefrom. I Y

4. In the separation of molybdenite from a mineral aggregate including other sulphides such as iron and copper sulphides, and gangue ma rials, by froth flotation, the improvement which comprises: subjecting such a mineral aggregate to an aging treatment to effect an oxidation of such other sulphides by heating such aggregate at a superatmospheric temperature in the presence of oxygen, said treatment being ineffective to cause substantial oxidation of such molybdenlte and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite; subjecting the aged aggregate to froth flotation at a pH less than 8 to produce a tailings product containing the principal proportion of the molybdenite present in such aggregate; and subsequently subjecting such tailings product to froth flotation at a pH higher than that obtaining in the first-mentioned froth flotation in the presence of a molybdenite collector to produce a float product consisting principally of molybdenite.

5. The improvement. set forth in claim 4, in which the aging treatment comprises roasting the aggregate at a temperature in the neighborhood of 300 to 700 F.

6. In the separation of molybdenite from a mineral aggregate including other sulphides such as iron and copper sulphides, and gangue materials, by froth flotation, the improvement which comprises: subjecting such a mineral aggregate to an aging treatment to effect an oxidation of such other sulphides by heating such aggregate at a superatmospheric temperature in the presence of oxygen, said heating treatment being ineffective to cause substantial oxidation of such molybdenite and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite; subjecting the so treated aggregate to froth flotation at a pH less than 8 to produce a tailings product containing the principal proportion of the molybdenite present in such aggregate; and subsequently subjecting such tailings product to from flotation in the presence of a molybdenite collector at a pH greater than that obtaining in the first-mentioned froth flotation and within the range of pH 3 to pH 11, to produce a float product consisting principally of molybdenite.

'7. In the separation of. molybdenite from a mineral aggregate including other sulphides such as iron and copper sulphides and gangue materials, by froth flotation, the improvement which comprises: subjecting such a mineral aggregate to an aging treatment to effect an oxidation of such other sulphides by heating such aggregate at a superatmospheric temperature in the presence of oxygen, said heating treatment being ineffective to cause substantial oxidation of such molybdenite and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite; subjecting the so treated aggregate to froth flotation in the presence of a' frothing agent comprising one or more aliphatic monohydric alcohols of from 2 to 12 carbon atoms, at a pH less than 8 to produce a tailings product containing the principal proportion of the molybdenite present in such aggregate; and subsequently subjecting such tailings product to froth flotation in the presence of a molybdenite collector and a frothing agent comprising one or more aliphatic monohydric alcohols of from 2 to 12 carbon atoms at a pH greater than that obtaining in the first-mentioned froth flotation and within the range of pH 3 to pH 11 to produce a float product coneffective to cause substantial oxidation of such molybdenite and eflective to materially depress the floatability of such other sulphides with respect to that of such molybdenite; subjecting the aged aggregate to froth flotation at a pI-I'less than 8 to produce a tallings product containing the principal proportion of the molybdenite present in such aggregate; and subsequently sub- J'ecting such tailings product to froth flotation at a pH higher than that obtaining in the flrstmentioned froth flotation but not in excess of pH 9, in the presence of a molybdenite collector,

pheric temperature in the presence of oxygen to effect an oxidation of such other sulphides, said treatment being ineffective to cause substantial oxidation of such molybdenite and' effective to materially depress the fioatability ofsuch other sulphides with respect to that of such molybdenite, and then subjecting the so heated aggregate to froth flotation in the presence'of a frothingagent comprising one or more aliphatic monohydric alcohols of from 2 to 12 carbon atoms, to separate the principal proportion of gangue materials therefrom.

' mineral aggregate including other sulphides such 11; The improvement set forth in claim 10, in

as iron and copper sulphides, and gangue mate rials, by froth flotation, the improvement which comprises: subjecting such a mineral I aggregate to an aging treatment to effect an oxidation of such other sulphides by heating such aggregate at a superatmospheric temperature in the presence of oxygen, said treatment being ineffective to cause substantial oxidation of such molybdenite and effective to materially depress the floatability of such other sulphides with respect to that of such molybdenite; subjecting the aged aggregate to froth flotation at a pH less than 8 and in the presence of a frothing agent comprising one or more aliphatic monohydric alcohols of from 2 to 12 carbon atoms, to produce a tailingsproduct containing the principal proportion of the molybdenite present in such aggregate; and subsequently subjecting such tailings product to froth flotation at a pH higher than that obtaining in the first-mentioned froth-flotation in the presence of a frothing agent comprising one or more aliphatic monohydric alcohols of from 2 to 12 carbon atoms, and a molybdenite collector, to produce a float product consisting principally of molybdenite.

13. The improvement set forth in claim 12, in which the aging treatment comprises roasting the aggregate at a temperature in the neighborhood of from 300 to 700 F., and in which the last-mentioned froth flotation is conducted at a pH not in excess of 11.

a THOMAS A. JANNEY. ALPHA G. JOHNSON. CHARLES M. NOKES. 

